Mark Whiting is a history teacher at Hitsue Middle School and later the supervisor of Hitsue High School's cardfight club.
An American with a rich love for Sengoku history, Mr. Mark is Aichi Sendou's history teacher at Hitsue Middle School, and opens the series with his narration on the Second Battle of Kawanakajima (1555) between Takeda Shingen and Uesugi Kenshin. Mr. Mark uses history trading cards in his classroom as a visual aid, and focuses on student participation to help with learning. Mr. Mark's teaching is essential to Aichi's character development, as it's his encouragement that leads Aichi to start seriously competing.
Outside of school, he operates under the alias of Ninja Master M.
Mark becomes a teacher at Hitsue High School and is also the faculty advisor for the school's Vanguard Club.
When Hitsue Middle School was overrun with Reverse Fighters, Mark appeared under the alias Ninja Master Neo. He held off the Reversed Nagisa so that Kamui could go rescue Emi. Nagisa backed Mark into a corner using Deadliest Beast Deity, Ethics Buster "Яeverse", but Mark scraped by with a Heal Trigger and won the fight with a Break Ride.
Mark was last seen participating in the shop tournament at Card Capital in the final episode of the original series, along with most of the other characters.
Aichi was following Morikawa when he stumbled upon CF research club. Aichi figured that it meant Cardfight though he never thought that there be a club like that in school in the first place. Then Mr. Whiting (Mr. Mark as everyone would refer him as) came around. He asked Aichi (Mr. Sendou as Mr. Mark refers him as) if he was planning to join the club as he is the advisor of it. He allowed Aichi in the club due to Aichi saying that he was interested. Mr. Mark had both good news and bad news to tell to the memebers of the club. First, Mr. Mark announced that Aichi is interested in joining the club. Of course, Morikawa was against Aichi be allowed in. Saying that he just started Vanguard and that his skills are just not good enough. Mr. Mark said that since Morikawa keep scaring members away from the club, it became smaller than what he would have like it to be (there are only 4 members in the club currently, most clubs generally have at least 5 or more members). Then Mr. Mark announced that the club will be no longer recognized by the school meaning the club will be shut down. Izaki asked why. He said quite loudly that he isn't worthy of being an advisor of a club if his students are failing his tests: Akahori scoring 35 points, Izaki scoring 25 points, Morikawa scoring 20 points, and Inenaga scoring 30 points. His failing point for his tests are 40 points and the club average is 27.5 points making the club below the 40 points. Izaki asked if the club's average is above the 40 points failing limit then the club won't have to close down in which Mr. Mark said yes that is correct. So Izaki asked about Aichi's current grade which Mr. Mark answered was 95 points. Izaki told Morikawa that with Aichi joining, the average would then be 41 points just one point above the failing point. Morikawa said that he rather not have Aichi in the club plus Mr. Mark also said that Mr. Sendou was only interested not really planning to join. Aichi then said that he will challege Morikawa in order to prove himself worthy of joining the club. Through Morikawa was not happy with this, Mr. Mark allowed them to cardfight. Aichi won which Mr. Mark said since he proved himself, Aichi was granted entrance in the club. Mr. Mark thought to himself that Cardfight was probably the best thing that ever happened to Aichi and was happy with how Aichi is slowly beginning to open himself up and gaining more confident in himself. He hoped that both him and Morikawa together will gain strength in their Cardfight skills.